Azelaic acid, derivatives and analogs thereof increase resistance to plant pathogens and prime plants to resist pathogen infection.
Plants activate both local and systemic defenses against many pathogens (virulent, avirulent and non-host) in responses that involve the induction of hundreds of genes. Thus, plants make a substantial investment in defense responses that help limit the growth of pathogens. Plant responses to many pathogens are often categorized as either compatible or incompatible, based on the degree of disease. In these two extremes, the pathogen typically either grows and causes extensive disease symptoms (the compatible case) or is relatively restricted in its replication (the incompatible case). In the case of incompatible responses (also called “resistance responses”), signaling is initiated by the perception of pathogen-derived Avirulence (Avr) proteins that interact directly or indirectly with cognate plant R proteins. Even in compatible interactions, it is now clear that the plant can often mount a defense response that is partially effective in limiting the pathogen. Global expression profiling after pathogen infection suggests that the compatible and incompatible responses largely affect the same sets of target genes, although the speed and degree to which they are induced is lower in the compatible case. A subset of these target genes is likely induced because it encodes important regulatory proteins that participate directly in signal transduction cascades or generates signal transduction intermediates. Understanding how these regulatory genes are activated under different conditions can give significant insight into signal flux through regulatory circuits.
The induction of salicylic acid (SA) synthesis is required for conferring resistance to a variety of compatible and incompatible pathogens. A number of mutants with reduced accumulation or signal transduction of SA also display increased susceptibility to pathogens like Pseudomonas syringae, a gram-negative extracellular pathogen.
In addition to being important for local defense responses, SA has been implicated in a whole-plant adaptive response to pathogens called systemic acquired resistance (SAR). After infection with an avirulent pathogen, SA accumulates in the systemic uninfected tissue. This systemic tissue shows increased resistance to many pathogens that would otherwise be highly virulent. Plants that cannot accumulate or perceive increased levels of SA in systemic tissues do not develop SAR. However, SA is thought not to be the key mobile defense signal in SAR and as yet unidentified signals generated during the defense response may also play a role in establishing SAR. Discovering the identity and properties of these unidentified signal molecules is important, as these are potential defense signals or signal intermediates.